1. Field of the Invention
Embodiments of the present invention generally relate to the fabrication of integrated circuits and particularly to the deposition of an amorphous carbon layer with high film density and high etch selectivity.
2. Description of the Related Art
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip design continually requires faster circuitry and greater circuit density. The demand for faster circuits with greater circuit densities imposes corresponding demands on the materials used to fabricate such integrated circuits. In particular, as the dimensions of integrated circuit components are reduced to sub-micron dimensions, it has been necessary to use not only low resistivity conductive materials such as copper to improve the electrical performance of devices, but also low dielectric constant insulating materials, often referred to as low-k materials. Low-k materials generally have a dielectric constant of less than 4.0.
Producing devices having low-k materials with little or no surface defects or feature deformation is problematic. Low-k dielectric materials are often porous and susceptible to being scratched or damaged during subsequent process steps, thus increasing the likelihood of defects being formed on the substrate surface. Low-k materials are often brittle and may deform under conventional polishing processes, such as chemical mechanical polishing (CMP). One solution to limiting or reducing surface defects and deformation of low-k materials is the deposition of a hardmask (e.g., TiN hardmask) over the exposed low-k materials prior to patterning and etching. The hardmask prevents damage and deformation of the delicate low-k materials. In addition, a hardmask layer may act as an etch mask in conjunction with conventional lithographic techniques to prevent the removal of a low-k material during etch.
Typically, the hardmask is an intermediate oxide layer, e.g., silicon dioxide or silicon nitride. However, some device structures already include silicon dioxide and/or silicon nitride layers, for example, damascene structures. Such device structures, therefore, cannot be patterned using a silicon dioxide or silicon nitride hardmask as an etch mask, since there will be little or no etch selectivity between the hardmask and the material thereunder, i.e., removal of the hardmask will result in unacceptable damage to underlying layers. To act as an etch mask for oxide layers, such as silicon dioxide or silicon nitride, a material must have good etch selectivity relative to those oxide layers.
Amorphous hydrogenated carbon, also referred to as amorphous carbon and denoted a-C:H, has been proved to be an effective material serving as a hardmask for oxide, nitride, poly-Si, or metal (e.g., Al) materials. Amorphous hydrogenated carbon is essentially a carbon material with no long-range crystalline order which may contain a substantial hydrogen content, for example on the order of about 10 to 45 atomic %. a-C:H is used as hardmask material in semiconductor applications because of its chemical inertness, optical transparency, and good mechanical properties. While a-C:H films can be deposited via various techniques, plasma enhanced chemical vapor deposition (PECVD) is widely used due to cost efficiency and film property tunability.
To ensure that the desired amorphous carbon film adequately protects underlying material layer during dry etching, it is important that amorphous carbon film possesses a relatively high etch selectivity, or removal rate ratio, with respect to material layer thereunder. Generally, an etch selectivity during the dry etch process of at least about 3:1 or more, such as 10:1, is desirable between amorphous carbon film and material layer, i.e., material layer is etched ten times faster than amorphous carbon film. In this way, the hardmask film formed by amorphous carbon protects regions of underlying material layer that are not to be etched or damaged while apertures are formed therein via a dry etch process.
The etch selectivity has been known can be increased with a higher film density. For amorphous carbon hardmask, however, there is typically a trade-off between high film density and hardmask ashability. It is therefore a need for an amorphous carbon hardmask which has higher film density (and therefore etch selectivity) while maintaining a decent ashability for hardmasks.